Platelet CĪ Inhibitor

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Selective Peripheral Dopamine-1 Receptor Slimulation with Fenoldopam in Human Essential Hypertension

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Role of calcium and phosphoinositides in the actions of certain hormones and neurotransmitters.

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J H Exton

Regulation of alpha 1 proteinase inhibitor function by rabbit alveolar macrophages. Evidence for proteolytic rather than oxidative inactivation.

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Rabbit alveolar macrophages were cultured in an environment conducive to the secretion of both reactive oxygen and proteinases, so that the relative importance of proteolytic and oxidative inactivation of alpha 1-proteinase inhibitor by alveolar macrophages could be evaluated. The inactivation of alpha 1-proteinase inhibitor was proportional to its proteolysis, and there was no detectable inactivation in the absence of proteolysis. Although the live macrophages were capable of secreting reactive oxygen, they did not inactivate alpha 1-proteinase inhibitor by oxidation. The inactivation of alpha 1-proteinase inhibitor by proteolysis was proportional to the secretion of elastinolytic activity by the alveolar macrophages. The inability of the alveolar macrophages to oxidize alpha 1-proteinase inhibitor was attributed to the methionine in the macrophages, in secreted proteins, and in the culture medium competing for oxidants. The data suggest that proteolytic inactivation of alpha 1-proteinase inhibitor may be important in vivo and that the methionine concentration in vivo may protect alpha 1-proteinase inhibitor from significant oxidative inactivation.

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M J Banda, E J Clark, Z Werb

Familial gynecomastia with increased extraglandular aromatization of plasma carbon19-steroids.

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We evaluated a family in which gynecomastia occurred in five males in two generations. In each affected subject, gynecomastia and male sexual maturation began at an early age. The ratio of the concentration of plasma estradiol-17 beta to that of plasma testosterone was elevated in each affected subject. In the three siblings with gynecomastia, the transfer constant of conversion of androstenedione to estrone (i.e., the fraction of plasma androstenedione that was converted to estrone as measured in the urine) was 10 times that of normal persons. The transfer constant of conversion of testosterone to estradiol-17 beta in the one subject studied also was 8-10 times that of normal men, whereas the transfer constants of conversion of estrone to estradiol-17 beta and of estradiol-17 beta to estrone were normal. Despite the elevation in extraglandular aromatase activity, there was a normal response of the hypothalamic-pituitary axis to provocative stimuli. This is the second documentation of gynecomastia that is associated with increased extraglandular aromatase activity, and the first time that the defect was found to be familial with a probable X-linked (or autosomal dominant, sex limited) mode of inheritance.

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G D Berkovitz, A Guerami, T R Brown, P C MacDonald, C J Migeon

Release of arachidonate from membrane phospholipids in cultured neonatal rat myocardial cells during adenosine triphosphate depletion. Correlation with the progression of cell injury.

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The present study utilized a cultured myocardial cell model to evaluate the relationship between the release of arachidonate from membrane phospholipids, and the progression of cell injury during ATP depletion. High-energy phosphate depletion was induced by incubating cultured neonatal rat myocardial cells with various combinations of metabolic inhibitors (deoxyglucose, oligomycin, cyanide, and iodoacetate). Phospholipid degradation was assessed by the release of radiolabeled arachidonate from membrane phospholipids. In this model, the current study demonstrates that (a) cultured myocardial cells display a time-dependent progression of cell injury during ATP depletion; (b) the morphologic patterns of mild and severe cell injury in the cultured cells are similar to those found in intact ischemic canine myocardial models; (c) cultured myocardial cells release arachidonate from membrane phospholipids during ATP depletion; and (d) using two separate combinations of metabolic inhibitors, there is a correlation between the release of arachidonate, the development of severe cellular and sarcolemmal damage, the release of creatine kinase into the extracellular medium, and the loss of the ability of the myocardial cells to regenerate ATP when the metabolic inhibitors are removed. Thus, the present results suggest that during ATP depletion, in cultured neonatal rat myocardial cells, the release of arachidonate from myocardial membrane phospholipids is linked to the development of membrane defects and the associated loss of cell viability.

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K R Chien, A Sen, R Reynolds, A Chang, Y Kim, M D Gunn, L M Buja, J T Willerson

Continuous administration of synthetic ovine corticotropin-releasing factor in man. Physiological and pathophysiological implications.

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The continuous 24-h infusion of a maximally stimulating dose (1 micrograms/kg per h) of ovine corticotropin-releasing factor (CRF) in man caused a modest elevation of plasma cortisol (17.2 +/- 1.4 micrograms/dl) and urinary-free cortisol (173 +/- 43 micrograms/24 h) concentrations, which was far less than that seen with a maximally stimulating dose of ACTH (50.4 +/- 2.2 micrograms/dl and 1,200 +/- 94 micrograms/24 h, respectively). The circadian rhythms of plasma ACTH and cortisol were preserved during CRF administration. An intravenous bolus injection of 1 microgram/kg of ovine CRF given to normal volunteers under basal conditions resulted in elevated plasma ACTH and cortisol peak levels (28 +/- 6 pg/ml and 15.0 +/- 1.0 micrograms/dl, respectively). However, no plasma ACTH and cortisol responses were observed when an identical CRF stimulation test was given at the end of the continuous infusion. These findings suggest that the stimulatory activity of exogenous CRF on the ACTH-secreting cells of the pituitary gland is restrained by the negative feedback of cortisol. The persistent circadian rhythm of ACTH, despite a constant level of plasma CRF during the infusion, suggests that the circadian variation in the activity of the hypothalamic-pituitary-adrenal axis cannot be explained solely by circadian periodicity of the endogenous CRF stimulus.

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H M Schulte, G P Chrousos, P W Gold, J D Booth, E H Oldfield, G B Cutler Jr, D L Loriaux

A circulating inhibitor of fluid-phase amplification. C3 convertase formation in systemic lupus erythematosus.

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C3 nephritic factor (C3NeF) was used to assess the formation of the fluid-phase amplification convertase, C3b,Bb, in 37 serum specimens from 24 patients with systemic lupus erythematosus (SLE). C3b,Bb formation was measured by the concentration of Ba, released when C3b,B is activated. Incubation of normal human serum (NHS) with C3NeF accelerates C3b amplification loop turnover with the formation of large quantities of C3b,Bb. In contrast, sera from 22 of 24 patients with SLE formed little or no convertase when incubated with C3NeF. C3 conversion to C3b was commensurately reduced. The inhibition could not be attributed to depressed serum concentrations of C3, factor B, or classical pathway components. Inhibitor present in excess could be demonstrated in 23 of 34 specimens of SLE serum by mixing experiments. The spontaneous convertase formation that occurs when a portion of the serum H is inactivated with F(ab')2 anti-H was also shown to be inhibited in SLE serum. The inhibition was found, however, to be H dependent in that convertase formation was normal in SLE serum depleted of H. It is concluded that the C3b in most SLE sera is unusually susceptible to inactivation by H, but a functional abnormality was not demonstrable in either C3 or H isolated from SLE serum. The inhibition could be simulated in NHS by addition of heparin, 100 micrograms/ml. In vivo, inhibition of convertase formation could interfere with the solubilization and disposal of immune complexes by reducing the deposition of C3b on the immune complex lattice.

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F B Waldo, J Forristal, L Beischel, C D West

Defective metabolism of hypertriglyceridemic low density lipoprotein in cultured human skin fibroblasts. Normalization with bezafibrate therapy.

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The metabolism of hypertriglyceridemic low density lipoprotein (HTG-LDL) was investigated in upregulated cultured human skin fibroblasts. Low density lipoprotein (LDL) was isolated by zonal centrifugation from the plasma of seven HTG subjects, before and 2 wk after the initiation of bezafibrate (BZ) therapy. HTG-LDL is a cholesterol-poor, triglyceride-rich lipoprotein of smaller diameter than BZ-LDL or normal LDL (N-LDL). Binding, cell association, and proteolytic degradation of HTG-LDL were compared with that of BZ-LDL and N-LDL and were found to be significantly lower by a paired t test analysis (P less than 0.001). After 6 h preincubation with unlabeled HTG-LDL, the incorporation of [14C]acetate to sterols was significantly higher than with BZ-LDL or N-LDL (577 +/- 43.7; 330 +/- 41.5; 262 +/- 47, mean +/- SE, picomoles sterols per milligram cell protein per 2 h, respectively; P less than 0.001 by paired t test). To determine the effectiveness of HTG-LDL and BZ-LDL on the down-regulation of LDL receptor activity, up-regulated cells were incubated for 48 h with HTG-LDL and BZ-LDL. LDL receptor activity was significantly higher after preincubation with HTG-LDL compared with BZ-LDL, and the rates of sterol synthesis were similarly increased. These results demonstrate that HTG-LDL does not down-regulate the LDL receptor activity as efficiently as BZ-LDL and that its cholesterol content is not enough to adequately suppress cellular sterol synthesis. Significant correlation between LDL composition and cholesterol synthesis by cultured cells was found with all LDL preparations over a wide range of cholesteryl ester to protein ratio (0.8-2.2). This correlation indicates that the compositional and structural abnormalities of HTG-LDL, and especially the low cholesterol content of the lipoprotein, alter LDL metabolism and cellular cholesterol formation.

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Y Kleinman, S Eisenberg, Y Oschry, D Gavish, O Stein, Y Stein

Characterization of high density lipoprotein binding to human adipocyte plasma membranes.

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Freshly isolated human adipocytes showed specific uptake of 125I-labeled human high density lipoprotein (HDL2 and HDL3), a portion of which could be released by subsequent incubation with excess unlabeled ligand. To study the mechanism of HDL binding, sucrose gradient-purified adipocyte plasma membranes were incubated with radioiodinated lipoprotein particles under equilibrium conditions in the absence (total binding) or presence (nonspecific binding) of 100-fold excess unlabeled ligand. Specific binding of HDL2 and HDL3, calculated by subtracting nonspecific from total binding, was Ca++ independent, unaffected by EDTA, and not abolished by pronase treatment of the membranes. Modification of HDL3 by reductive methylation or cyclohexanedione treatment also failed to affect its binding to adipocyte plasma membranes. High salt concentration (200 mM NaCl) inhibited specific binding of HDL2 and HDL3 but had no effect on LDL binding. A significant portion of 125I-HDL2 or 125I-HDL3 binding was consistently inhibited by adding excess unlabeled LDL, but this inhibition was incomplete as compared with a similar molar excess of unlabeled HDL2 or HDL3. The role of apoproteins (apo) in HDL binding to adipocyte membranes was examined by comparing binding of HDL2 and HDL3 isolated from normal, abetalipoproteinemic (abeta) and apo E-deficient (apo E0) plasma. Specific binding was observed with all normal and mutant HDL particles. Furthermore, a significant portion (61-78%) of abeta-HDL2, apo E0-HDL2, and apo E0-HDL3 binding was inhibited by adding 100-fold excess of unlabeled low density lipoproteins (LDL). The cross-competition of LDL and HDL binding was confirmed by the ability of normal, abeta, and apo E0-HDL2 to completely inhibit 125I-LDL binding. These data suggest that HDL binding is independent of apo E and that the responsible apoprotein(s) of HDL complete with LDL-apo B for binding to the same or closely related site in the adipocyte plasma membrane. Normal and apo E0-HDL3 binding was also completely inhibited by normal HDL2, which suggested that HDL2 and HDL3 probably bind to the same site. Scatchard analysis of normal HDL2, normal HDL3, and apo E0-HDL3 binding data best fitted a one-component binding profile with similar equilibrium dissociation constants (40-96 nM). HDL3 binding was found to be effectively inhibited by anti-human apo AI or anti-human apo AII, but not by anti-human apo B antisera. This binding was also unaffected by monoclonal anti-human apo B or E antibodies known to inhibit binding of apo B or apo E containing lipoprotein to the LDL receptor of cultured fibroblasts. These findings, taken together, suggest that human fat cells possess HDL binding sites with apo AI and /or apo AII specificity. The significant but partial inhibition of HDL2 and HDL3 binding by LDL along with the complete inhibition of LDL binding by HDL2 and HDL3 tends to exclude a single binding site that interacts both lipoproteins and favors the interpretation that LDL and HDL particles bind to multiple recognition sites or to different conformation of the same lipoprotein binding domain on the human fat cell.

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B S Fong, P O Rodrigues, A M Salter, B P Yip, J P Despres, A Angel, R E Gregg

Race and sex differences in erythrocyte Na+, K+, and Na+-K+-adenosine triphosphatase.

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Several reports indicate that erythrocytes (RBCs) from blacks and men have higher sodium concentrations than those from whites and women. One possible mechanism to explain this finding is a difference in the activity of Na+-K+-ATPase. To explore this possibility, we have studied the Na+ and K+ kinetics of RBC Na+-K+-ATPase and RBC Na+ and K+ concentrations in 37 normotensive blacks and whites, both males and females. The maximal initial reaction velocity (Vmax) values for RBC Na+-K+-ATPase were lower in blacks and men as compared with whites and women. Higher RBC Na+ levels were observed in blacks and males vs. whites and females. Significant inverse correlations were noted between the Na+-K+-ATPase activity and RBC Na+ concentrations. These findings indicate that cellular Na+ homeostasis is different in blacks and men as compared with whites and women. Since higher RBC Na+ concentrations have also been observed in patients with essential hypertension as compared with normotensive subjects, the higher intracellular Na+ concentrations in blacks and men may contribute to the greater predisposition of these groups to essential hypertension.

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N Lasker, L Hopp, S Grossman, R Bamforth, A Aviv

Antibody-mediated killing of suppressor T lymphocytes as a possible cause of macroglobulinemia in the tropical splenomegaly syndrome.

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To investigate the pathogenesis of macroglobulinemia in the tropical splenomegaly syndrome (TSS), we assessed the functional activity of B lymphocytes and T cell subsets in a pokeweed mitogen-driven assay of immunoglobulin synthesis. Mononuclear cells from patients with TSS produced more IgM than cells from village or from distant controls. This appeared to result from a decrease in the number and/or activity of suppressor T cells of the T8+ phenotype. The lack of functional suppressor T lymphocytes was associated with the presence in sera from patients with TSS of IgM antibodies that specifically killed T8+, 9.3-, 60.1+ T cells from normal donors. These results support the hypothesis that macroglobulinemia in TSS results from defective immunoregulatory control of B cell function, and that this may be caused by lysis of suppressor T cells by specific lymphocytotoxic antibodies produced by patients with this syndrome.

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W F Piessens, S L Hoffman, A A Wadee, P W Piessens, S Ratiwayanto, L Kurniawan, J R Campbell, H A Marwoto, L L Laughlin

Deficiency of the autologous mixed lymphocyte reaction in patients with classic hemophilia treated with commercial factor VIII concentrate. Correlation with T cell subset distribution, antibodies to lymphadenopathy-associated or human T lymphotropic virus, and analysis of the cellular basis of the deficiency.

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14 patients with hemophilia were studied for the distribution of T cell subsets, the presence of antibody to lymphadenopathy-associated or human T lymphotropic virus type III (LAV/HTLV-III), and their responsiveness in autologous mixed lymphocyte reactions. In addition, mitogen and alloantigen responsiveness and Interleukin-2 production were investigated. Seven patients were found to have low Leu 3a/Leu 2a (T4/T8) ratios; eight patients had antibody to LAV/HTLV-III; and an additional patient had acquired immunodeficiency syndrome. Responsiveness to mitogens and alloantigens as well as Interleukin-2 production were comparable with those of healthy individuals. However, patients with low ratio, many of whom had antibodies to LAV/HTLV-III, had a highly deficient autologous mixed lymphocyte reaction. This reduced response of T cells to autologous non-T cells could not be corrected by elimination of Leu 2a/T8 cells, which indicated that there was a preferential loss of the Leu 3a cell subset(s) which responded to autologous non-T cells. Thus, these patients have a deficiency of intercellular communication within their immune system.

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J S Smolen, P Bettelheim, U Köller, S McDougal, W Graninger, T A Luger, W Knapp, K Lechner

Effects of antioxidants on oxidant-induced sister chromatid exchange formation.

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Stimulated human phagocytes produce sister chromatid exchanges in cultured mammalian cells by a mechanism involving oxygen metabolites. Experiments were designed to determine whether antioxidants inhibit this process. Superoxide dismutase, catalase, and hydroxyl radical scavengers (benzoate, mannitol) protected target Chinese hamster ovary cells from phagocyte-induced sister chromatid exchanges, implicating the involvement of hydroxyl radicals in this chromosomal damage. N-acetylcysteine and beta-carotene were also protective. alpha-Tocopherol (greater than 5 microM) protected target cells exposed to phagocytes but not to enzymatically generated oxidants when the vitamin was added just before the source of oxygen radicals, suggesting, as reported by others, that the principal action of tocopherol in this setting was to inhibit the release of oxidants from phagocytes. On the other hand, cultivation of target cells with supplemental tocopherol protected them from the toxic effects of the enzymatic oxidant-producing system, indicating a role for membrane-associated free radicals in the mechanism of sister chromatid exchange induction. Low concentrations of sodium selenite (0.1-1.0 microM) protected the target cells. However, higher concentrations (10 microM) of selenite had no effect on oxidant-induced sister chromatid exchange formation, and 0.1 mM selenite increased the number of exchanges. Sodium selenite concentrations of 0.1 mM also decreased the intracellular glutathione concentration of target cells during an oxidant stress, and reducing target cell glutathione concentrations with buthionine sulfoximine increased their sensitivity to oxygen-related chromosomal damage. Therefore, the potentiation of oxygen radical-induced chromosomal damage observed with high concentrations of selenite may result from a decrease in the thiol antioxidant defense systems within the cell. The findings suggest that the hydroxyl radical has an important role in the production of phagocyte-induced cytogenetic injury, membrane-derived intermediates may be involved, depletion of intracellular glutathione renders cells more susceptible to this injury, and supplementation of target cells with antioxidants can protect them from oxygen radical-generated chromosomal injury.

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A B Weitberg, S A Weitzman, E P Clark, T P Stossel

Enhanced glycemic responsiveness to epinephrine in insulin-dependent diabetes mellitus is the result of the inability to secrete insulin. Augmented insulin secretion normally limits the glycemic, but not the lipolytic or ketogenic, response to epinephrine in humans.

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To determine if the enhanced glycemic response to epinephrine in patients with insulin-dependent diabetes mellitus (IDDM) is the result of increased adrenergic sensitivity per se, increased glucagon secretion, decreased insulin secretion, or a combination of these, plasma epinephrine concentration-response curves were determined in insulin-infused (initially euglycemic) patients with IDDM and nondiabetic subjects on two occasions: once when insulin and glucagon were free to change (control study), and again when insulin and glucagon were held constant (islet clamp study). During the control study, plasma C-peptide doubled, and glucagon did not change in the nondiabetic subjects, whereas plasma C-peptide did not change but glucagon increased in the patients. The patients with IDDM exhibited threefold greater increments in plasma glucose, largely the result of greater increments in glucose production. This enhanced glycemic response was apparent with 30-min increments in epinephrine to plasma concentrations as low as 100-200 pg/ml, levels that occur commonly under physiologic conditions. During the islet clamp study (somatostatin infusion with insulin and glucagon replacement at fixed rates), the heightened glycemic response was unaltered in the patients with IDDM, but the nondiabetic subjects exhibited an enhanced glycemic response to epinephrine indistinguishable from that of patients with IDDM. In contrast, the FFA, glycerol, and beta-hydroxybutyrate responses were unaltered. Thus, we conclude the following: Short, physiologic increments in plasma epinephrine cause greater increments in plasma glucose in patients with IDDM than in nondiabetic subjects, a finding likely to be relevant to glycemic control during the daily lives of such patients as well as during the stress of intercurrent illness. Enhanced glycemic responsiveness of patients with IDDM to epinephrine is not the result of increased sensitivity of adrenergic receptor-effector mechanisms per se nor of their increased glucagon secretory response; rather, it is the result of their inability to augment insulin secretion. Augmented insulin secretion, albeit restrained, normally limits the glycemic response, but not the lipolytic or ketogenic responses, to epinephrine in humans.

Authors

M A Berk, W E Clutter, D Skor, S D Shah, R P Gingerich, C A Parvin, P E Cryer

Despite a massive increase in cortisol secretion in women during parturition, there is an equally massive increase in prostaglandin synthesis. A paradox?

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In this investigation, we sought to resolve the apparent paradox that is posed by the fact that there is a simultaneous increase in the production of prostaglandin and cortisol in women during labor. A paradox obtains, since in most tissues, cortisol acts to inhibit prostaglandin formation. Using previously characterized model systems for the in vitro study of arachidonic acid metabolism in amnion, decidua, and myometrium, we found that prostaglandin production by amnion and endometrial stromal cells in monolayer culture was not decreased by glucocorticosteroid treatment. On the other hand, prostaglandin production by myometrial smooth muscle cells in culture was inhibited by greater than 90% in response to dexamethasone (10(-7) M) treatment. Importantly, the major prostaglandin produced by myometrium, as well as myometrial smooth muscle cells in culture, is prostacyclin, a prostaglandin that acts to cause uterine quiescence. We suggest that the immunity of amnion and decidua to the action of glucocorticosteroids may allow for the accelerated production of prostaglandins E2 and F2 alpha, which act to cause myometrial contractions; simultaneously, glucocorticosteroid produced in large quantities in women in labor may lead to decreased production of prostacyclin by myometrium, thereby reducing uterine quiescence. In this coordinated manner, the uterine contractions that culminate in delivery of the fetus may proceed uninterrupted in the face of increased cortisol production.

Authors

M L Casey, P C MacDonald, M D Mitchell

Healing of bone disease in X-linked hypophosphatemic rickets/osteomalacia. Induction and maintenance with phosphorus and calcitriol.

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Although conventional therapy (pharmacologic doses of vitamin D and phosphorus supplementation) is usually successful in healing the rachitic bone lesion in patients with X-linked hypophosphatemic rickets, it does not heal the coexistent osteomalacia. Because serum 1,25-dihydroxyvitamin D levels are inappropriately low in these patients and high calcitriol concentrations may be required to heal the osteomalacia, we chose to treat five affected subjects with high doses of calcitriol (68.2 +/- 10.0 ng/kg total body weight/d) and supplemental phosphorus (1-2 g/d) performing metabolic studies and bone biopsies before and after 5-8 mo of this therapy in each individual. Of these five patients, three (aged 13, 13, and 19 yr) were receiving conventional treatment at the inception of the study and therefore showed base-line serum phosphorus concentrations within the normal range. The remaining two untreated patients (aged 2 and 37 yr) displayed characteristic hypophosphatemia before calcitriol therapy. All five patients demonstrated serum calcitriol levels in the low normal range (22.5 +/- 3.2 pg/ml), impaired renal phosphorus conservation (tubular maximum for the reabsorption of phosphate per deciliter of glomerular filtrate, 2.13 +/- 0.20 mg/dl), and osteomalacia on bone biopsy (relative osteoid volume, 14.4 +/- 1.7%; mean osteoid seam width, 27.7 +/- 3.7 micron; mineral apposition rate, 0.46 +/- 0.12 micron/d). On high doses of calcitriol, serum 1,25-dihydroxyvitamin D levels rose into the supraphysiologic range (74.1 +/- 3.8 pg/ml) with an associated increment in the serum phosphorus concentration (2.82 +/- 0.19 to 3.78 +/- 0.32 mg/dl) and improvement of the renal tubular maximum for phosphate reabsorption (3.17 +/- 0.22 mg/dl). The serum calcium rose in each patient while the immunoactive parathyroid hormone concentration measured by three different assays remained within the normal range. Most importantly, repeat bone biopsies showed that high doses of calcitriol and phosphorus supplements had reversed the mineralization defect in all patients (mineral apposition rate, 0.88 +/- 0.04 micron/d) and consequently reduced parameters of bone osteoid content to normal (relative osteoid volume, 4.1 +/- 0.7%; mean osteoid seam width, 11.0 +/- 1.0 micron). Complications (hypercalcemia and hypercalciuria) ensued in four of these five patients within 1-17 mo of documented bone healing, necessitating reduction of calcitriol doses to a mean of 1.6 +/- 0.2 micrograms/d (28 +/- 4 ng/kg ideal body weight per day). At follow-up bone biopsy, these four subjects continued to manifest normal bone mineralization dynamics (mineral apposition rate, 0.88 +/-0.10 micrometer/d) on reduced doses of 1.25-dihydroxyvitamin D with phosphorus supplements (2 g/d) for a mean of 21.3 +/- 1.3 mo after bone healing was first documented. Static histomorphometric parameters also remained normal (relative osteoid volume, 1.5 +/- 0.4%; mean osteoid seam width, 13.5 +/- 0.8 micrometer). These data indicate that administration of supraphysiologic amounts of calcitriol, in conjunction with oral phosphorus, results in complete healing of vitamin D resistant osteomalacia in patients with X-linked hypophosphatemic rickets. Although complications predictably require calcitriol dose reductions once healing is achieved, continued bone healing can be maintained for up to 1 yr with lower doses of 1,25-dihydroxyvitamin D and continued phosphorus supplementation.

Authors

R M Harrell, K W Lyles, J M Harrelson, N E Friedman, M K Drezner

Pathogenesis of nephrogenic diabetes insipidus due to chronic administration of lithium in rats.

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A polyuric syndrome with nephrogenic diabetes insipidus (NDI) is a frequent consequence of prolonged administration of lithium (Li) salts. Studies in the past, mainly the acute and in vitro experiments, indicated that Li ions can inhibit hydroosmotic effect of [8-arginine]vasopressin (AVP) at the step of cAMP generation in vitro. However, the pathogenesis of the NDI due to chronic oral administration of low therapeutic doses of Li salts is not yet clarified. We conducted a comprehensive study to clarify the mechanism by which Li administered orally for several weeks induces polyuria and NDI in rats. Albino rats consuming a diet which contained Li (60 mmol/kg) for 4 wk developed marked polyuria and polydipsia; at the end of 4 wk the plasma Li was 0.7 +/- 0.09 mM (mean +/- SEM; n = 36). Li-treated rats had a significantly decreased (-33%) tissue osmolality in papilla and greatly reduced cortico-papillary gradient of urea (cortex--43%; medulla--64%; papilla--74%). Plasma urea was significantly (P less than 0.001) lower in Li-treated rats (5.4 +/- 0.2 mM) compared with controls (6.8 +/- 0.3 mM). Medullary collecting tubules (MCT) and papillary collecting ducts (PCD) microdissected from Li-treated animals had higher content of protein than MCT and PCD from the control rats. The cAMP accumulation in response to AVP added in vitro was significantly (delta = -60%) reduced. Also, the cAMP accumulation in MCT and PCD after incubation with forskolin was markedly lower in Li-treated rats. Addition of 0.5 mM 1-methyl,3-isobutyl-xanthine did not restore the cAMP accumulation in response to AVP and forskolin in MCT from Li-treated animals. In collecting tubule segments from polyuric rats with hypothalamic diabetes insipidus (Brattleboro homozygotes) the AVP-dependent cAMP accumulation was not diminished. The activity of adenylate cyclase (AdC) in MCT of Li-treated rats, both the basal and the activity stimulated by AVP, forskolin, or fluoride, was significantly (delta approximately equal to -30%) reduced, while the activity of cAMP phosphodiesterase (cAMP-PDIE) in the same segment showed no significant difference from the controls. Also, the content of ATP in MCT microdissected from Li-treated rats and incubated in vitro did not differ from controls. The rate of [14C]succinate oxidation to 14CO2 in MAL was inhibited (-77%) by 1 mM furosemide, which indicates that this metabolic process is coupled with NaCl cotransport in MAL. The rate of (14)CO(2) production from [14C]succinate in MAL was not significantly different between control and Li-treated rats. In MCT of control rats, the rate of [14C]succinate oxidation was approximately 3 times lower than in MAL. The rate of (14)CO(2) production from [(14)C]succinate in MCT of Li-treated rats was significantly (delta +33%) higher than in MCT dissected from control rats. Based on these results, we conclude that at least two factors play an important role in the pathogenesis of NDI consequent to chronic oral administration of Li: (a) decreased ability of MCT and PCD to generate and accumulate cAMP in response to stimulation by AVP; this defect is primarily due to diminished activity of AdC in these tubular segments caused by prolonged exposure to Li; and (b) lower osmolality of renal papillary tissue, due to primarily to depletion of urea, which decreases osmotic driving force for water reabsorption in collecting tubules. On the other hand, NaCI reabsorption in MAL is apparently not affected by chronic Li treatment.

Authors

S Christensen, E Kusano, A N Yusufi, N Murayama, T P Dousa

Characterization of precursor and secreted forms of human angiotensinogen.

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To define the basis of the heterogeneity of angiotensinogen, we have characterized the immunoreactivity of high molecular weight (HMW) and low molecular weight (LMW) plasma angiotensinogen, the angiotensinogen precursor synthesized by cell-free translation, and angiotensinogen secreted by human hepatoma (Hep G2) cells. Angiotensinogen precursor synthesized by rabbit reticulocyte lysate primed with RNA prepared from liver or Hep G2 cells was compared with angiotensinogen secreted by Hep G2 cells by using immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). So as to assess the contribution of N-glycosylation of angiotensinogen, Hep G2 cells were incubated in the presence of tunicamycin. Glycosylation of secreted angiotensinogen was further characterized by using chromatography on concanavalin A-Sepharose, digestion with neuraminidase, and treatment with trifluoromethane sulfonic acid. In Sephadex G-200 column chromatography, HMW plasma angiotensinogen eluted just after the column void volume and was clearly separated from LMW angiotensinogen which eluted just before bovine serum albumin. Both HMW and LMW plasma angiotensinogen were shown to bind to monoclonal and polyclonal antibodies raised against pure LMW angiotensinogen. Only one angiotensinogen precursor (mol wt 50,000) was identified by cell-free translation which, after cleavage by renin, was reduced to mol wt 45,600. Angiotensinogen secreted by Hep G2 cells showed electrophoretic heterogeneity (mol wt 53,100-65,400). Tunicamycin-treated Hep G2 cells secreted five discrete forms of angiotensinogen, a predominant form of mol wt 46,200, with other forms (mol wt 46,800, 48,100, 49,200, and 49,600) representing 10% of secreted angiotensinogen. All five forms showed a similar reduction in molecular weight after cleavage by renin. The predominant 46,200-mol wt protein represented nonglycosylated angiotensinogen in that, after cleavage by renin, it had an electrophoretic mobility (mol wt 45,600) identical to the desangiotensin I-angiotensinogen resulting from renin cleavage of the angiotensinogen precursor. The other higher molecular weight forms of angiotensinogen secreted by tunicamycin-treated Hep G2 cells were shown to represent O-glycosylated angiotensinogen in that they were reduced to 46,200 mol wt by treatment with trifluoromethane sulfonic acid. Dexamethasone (10(-7) and 10(-6)M) stimulated angiotensinogen secretion by Hep G2 cells two- to fourfold, both in the absence and presence of tunicamycin. However, a small stimulatory effect of mestranol (10(-7) M) was evident only in the presence of tunicamycin. Neither dexamethasone nor mestranol influenced the electrophoretic pattern (SDS-PAGE) of angiotensinogen secreted by Hep G2 cells. However, when incubation media were chromatographed on Sephadex G-200 with subsequent immunoprecipitation of the column fractions, both dexamethasone and mestranol were shown to stimulate the secretion of HMW angiotensinogen (eluting just after the column void volume) which, on SDS-PAGE, migrated in a position identical to LMW angiotensinogen. From these studies, we conclude that all forms of human angiotensinogen are derived from a single precursor. The heterogeneity of secreted angiotensinogen represents differences in posttranslational processing of angiotensinogen. This processing includes both N- and O-glycosylation, and also the formation of HMW complexes (HMW angiotensinogen) through association either with other angiotensinogen molecules or with some other protein(s) whose secretion by hepatocytes is stimulated by glucocorticoids and estrogens.

Authors

D J Campbell, J Bouhnik, E Coezy, J Menard, P Corvol

Influence of naloxone on the total capacitance vasculature of the dog.

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Abstract

The opiate antagonist, naloxone, which is associated with prolonged survival in animal models of shock, has been demonstrated to increase arterial pressure and cardiac output. It is possible that the increase in cardiac output is due to a decrease in volume in the total capacitance vasculature and a subsequent increase in venous return. Because the influence of naloxone on the capacitance vasculature is unknown, the present study was undertaken to determine the influence of naloxone on intravascular volume in the total capacitance circulation. In 31 anesthetized dogs, blood from the vena cavae was drained into an extracorporeal reservoir and returned to the right atrium at a constant rate so that changes in total intravascular volume could be measured as reciprocal changes in reservoir volume. In five animals, naloxone infusion (2 mg/ml X min for 20 min) was associated with a decrease in total capacitance volume of 121 +/- 30 ml (P less than 0.05). To determine regional volume effects, naloxone was infused in 11 animals in which the splanchnic and extrasplanchnic vasculatures were separately perfused and drained: total and splanchnic volume decreased 64 +/- 13 ml (P less than 0.05) and 126 +/- 17 ml (P less than 0.0001), respectively, and extrasplanchnic volume increased 62 +/- 13 ml (P less than 0.001). After ganglionic blockade with mecamylamine (n = 3), total volume decreased 89 +/- 16 ml (P less than 0.05), splanchnic volume did not change, and extrasplanchnic volume decreased 91 +/- 32 ml (P less than 0.05). In another five animals, naloxone was infused during diversion of the splanchnic venous outflow to a nonrecirculating extracorporeal reservoir: total volume decreased 122 +/- 33 ml (P less than 0.05), splanchnic volume did not change, and extrasplanchnic volume decreased 101 +/- 16 ml (P less than 0.01). When the splanchnic venous effluent was reinfused without naloxone administration (n = 4), total volume decreased 43 +/- 5 ml (P less than 0.05), splanchnic volume decreased 113 +/- 14 ml (P less than 0.05), and extrasplanchnic volume increased 68 +/- 10 ml (P less than 0.05). Thus, naloxone is associated with a decrease in total capacitance volume, which is due entirely to a decrease in splanchnic volume. The splanchnic volume decrement would appear to be mediated through neurogenic and hormonal influences. In an animal not on bypass, it would be expected that naloxone would be associated with a decrease in total capacitance volume and subsequent increases in venous return and cardiac output.

Authors

L Bell, E Maratea, D L Rutlen

Passive transfer of diabetes from BB/W to Wistar-Furth rats.

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Abstract

Autoimmune diabetes can be transferred to young, diabetes prone BB/W rats by injecting them intravenously with concanavalin A (Con A)-treated spleen cells from acute diabetic BB/W donors. This study describes the transfer of diabetes to the normal Wistar-Furth strain of rats using a similar procedure. For the successful transfer of diabetes it was necessary to immunosuppress recipient animals with a single intraperitoneal injection of cyclophosphamide 24-48 h before administering Con A-stimulated spleen cells from acute diabetic BB/W rats. Of 68 Wistar-Furth rats in immunosuppressed with a dose of 100-150 mg cyclophosphamide/kg body wt, 10 (15%) became diabetic. None of the control rats receiving either Con A-stimulated Wistar-Furth spleen cells (n = 28), freshly isolated BB/W spleen cells (n = 14), or fresh RPMI medium (n = 11) became diabetic. These data indicate that diabetes can be transferred from BB/W to Wistar-Furth rats. In addition, they support the hypothesis that cell-mediated immune processes are involved in the development of insulin-dependent diabetes and rule out any absolute requirement for BB-derived genes in the target pancreatic beta cells.

Authors

S B Koevary, D E Williams, R M Williams, W L Chick

Low doses of interferon alpha result in more effective clinical natural killer cell activation.

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Abstract

To define critical parameters concerning interferon (IFN) effects upon natural killer (NK) cells in vivo, we gave cancer patients serial weekly intramuscular injections of purified lymphoblastoid IFN in six doses ranging from 10(5) to 3 X 10(7) U. Dose sequences were determined by randomly allocating patients to one of six levels in a latin square ordering scheme. NK cell stimulation, a threefold peak increase above preinjection levels of cytolysis (P = 0.022), occurred in peripheral mononuclear cells (PMC) sampled 24 h postinjection, of 3 X 10(6) U, but was not detectable at any dose in PMC sampled 7 d postinjection. No blunting occurred in NK cell responsiveness to repeated injection of IFN dosages a second time at or several weeks after study completion. At IFN doses of 3 X 10(6), 10(7), and 3 X 10(7) U, a negative correlation existed between the amount of IFN injected and the average extent of NK cell activation (r = -0.423, P less than 0.05). This contrasted with the progressively increasing response of NK cells to in vitro incubation with increasing concentration of up to 3,000 U/ml of IFN. Overnight culturing of PMC sampled before IFN injections resulted in a mean 1.9-fold increase in cytolytic activity (P = 0.0005) and a mean 53% decrease in variance (P = 0.024) between serial preinjection NK cell activity determinations. Cell separation procedures may, therefore, have resulted in NK cell inactivation, from which overnight culturing permitted recovery. We found that maximal NK cell activation at a low IFN dose, decreasing NK cell responsiveness at higher doses, and the need to culture PMC to efficiently detect NK cell boosting may account for disparities in reported effects of IFN on NK cell function.

Authors

B S Edwards, J A Merritt, R C Fuhlbrigge, E C Borden

Evidence for a functional role of endogenously produced somatomedinlike peptides in the regulation of DNA synthesis in cultured human fibroblasts and porcine smooth muscle cells.

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Abstract

Cultured porcine aortic smooth muscle cells and human fibroblasts produce somatomedinlike peptides and secrete them into the surrounding microenvironment. This production has been linked to their ability to replicate. The objective of this study was to determine if a specific anti-somatomedin-C (Sm-C) monoclonal antibody that binds the somatomedinlike peptides could inhibit replication by porcine aortic smooth muscle cells and human fibroblasts. To determine if the antibody could inhibit the effect of endogenously produced somatomedinlike peptide, increasing concentrations of antibody were co-incubated with platelet-derived growth factor, a known stimulant of somatomedinlike peptide secretion, and Sm-C-deficient platelet-poor plasma. Addition of the antibody reduced fibroblast [3H]thymidine incorporation from 35,100 +/- 500 to 10,600 +/- 700 cpm (P less than 0.001), and in smooth muscle cells from 29,600 +/- 1,800 to 10,800 +/- 1,100 cpm (P less than 0.001). Co-incubation of exogenously added Sm-C (20 ng/ml) with maximally inhibitory dilutions of antibody increased [3H]thymidine incorporation in fibroblasts from 7,800 +/- 1,000 to 18,900 +/- 800 cpm (P less than 0.01), and in smooth muscle cells from 9,800 +/- 1,200 to 17,200 +/- 1,100 cpm (P less than 0.01). Insulin, which can substitute for Sm-C as a mitogen and does not bind to the antibody, stimulated DNA synthesis when co-incubated with the antibody, thereby excluding the possibility of nonspecific cytotoxicity. These results strengthen the hypothesis that the rate of DNA synthesis of these two cell types in vitro is directly linked to their capacity to produce somatomedinlike peptides. They further support the cellular production of somatomedinlike peptides as examples of the autocrine model of growth regulation.

Authors

D R Clemmons, J J Van Wyk

Erythrocyte membrane rigidity induced by glycophorin A-ligand interaction. Evidence for a ligand-induced association between glycophorin A and skeletal proteins.

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Abstract

Erythrocyte skeletal proteins are known to play an important role in determining membrane deformability. In order to see whether transmembrane proteins also influence deformability and, if so, whether this influence is mediated by an interaction with the membrane skeleton, we examined the effect on deformability of ligands specific for transmembrane proteins. We found membrane deformability markedly reduced in erythrocytes that were pretreated with glycophorin A-specific ligands. In contrast, ligands specific for band 3 and A and B blood group antigens had no effect. The increase in membrane rigidity appeared to depend upon a transmembrane event and not upon a rigidity-inducing lattice on the outside surface of the cell in that a monovalent Fab of antiglycophorin IgG caused decreased deformability. We therefore looked for a ligand-induced association of glycophorin and the skeletal proteins and found, in Triton X-100-insoluble residues, a partitioning of glycophorin with the skeletal proteins only after preincubation with a ligand specific for glycophorin. We then studied cells and resealed membranes with skeletal protein abnormalities. In spectrin-deficient and protein 4.1-deficient erythrocytes and in 2,3-diphosphoglycerate-treated resealed membranes, the antiglycophorin IgG was only one-third as effective in decreasing deformability as it was in normal cells. Thus, normal skeletal proteins appear to be essential for liganded glycophorin to affect membrane deformability maximally. Taken together, these observations indicate that there is a ligand-induced interaction between glycophorin A and skeletal proteins and that this interaction can directly influence membrane deformability.

Authors

J A Chasis, N Mohandas, S B Shohet

Fuel-mediated teratogenesis. Use of D-mannose to modify organogenesis in the rat embryo in vivo.

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Abstract

The unique embryotoxic properties of D-mannose have been used as the basis for a new technique to secure precise temporal correlations between metabolic perturbations during organogenesis and subsequent dysmorphogenesis. Conscious, pregnant rats were infused with D-mannose or equimolar amounts of D-glucose by "square wave" delivery during the interval in which the neural plate is established and early fusion of neural folds takes place, that is, days 9.5-10.0 of gestation. Infusions of mannose to maternal plasma levels of 150-200 mg/dl did not elicit any toxicity in the mothers: motor activity, eating behavior, and serum components (electrolytes, osmolality, bilirubin) did not differ in glucose- vis-à-vis mannose-infused dams. Embryos were excised by hysterotomy on day 11.6 for evaluation of development. Examination with a dissecting microscope did not disclose developmental abnormalities in any of the 136 embryos from glucose-infused mothers or in 62 additional embryos from mothers that had not received any infusions. By contrast, dysmorphic changes were seen in 17 of 191 embryos (8.9%) from mannose-infused mothers. 14 of the 17 had abnormal brain or neural tube development with incomplete neural tube closure in 9 instances. Abnormal axial rotation was present in 8 of the 191 embryos (4.2%) and lesions of the heart or optic vesicles were seen in 4 (2.1%) and 3 (1.6%), respectively. Embryos from mannose-infused mothers displayed significant retardations in somite number, crown-rump length, and total protein and DNA content. These stigmata of growth retardation were more marked in the 17 dysmorphic embryos. The experiments indicate that D-mannose may be employed in model systems with rodents for precisely timed interruptions of organogenesis in vivo. Initial applications are consistent with our earlier suggestion that multiple dysmorphic changes may supervene after interference with communally observed metabolic dependencies during organogenesis. The studies do not identify the vulnerable site(s) within the conceptus (e.g., investing membranes, embryos, or both). However, the findings suggest that dysmorphic events are manifest most markedly in a general setting of embryo growth retardation.

Authors

T Buchanan, N Freinkel, N J Lewis, B E Metzger, S Akazawa

Correlation between G2m(n) immunoglobulin allotype and human antibody response and susceptibility to polysaccharide encapsulated bacteria.

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Abstract

To determine whether genetic factors influence the human antibody response to polysaccharides, we correlated Ig allotypes with the concentrations of antibody to 14 bacterial capsular antigens in 130 actively immunized Caucasian adults. The 88 individuals possessing G2m(n), an allotype antigen of IgG2 subclass heavy chains, had significantly higher postimmunization antibody levels to Haemophilus influenzae type b (Hib) and 8 of 11 pneumococcal types (P less than 0.05) than the 42 lacking this antigen. For Hib, pneumococcus type 14, and meningococcus group C, an increased response was observed in IgG class but not in IgM or IgA classes of antibody. The G2m(n) positive individuals also had higher preimmunization antibody levels to most polysaccharide antigens. Total IgG2 concentrations were correlated with the mean postimmunization antibody concentrations to pneumococci (P = 0.005), but this correlation was independent of G2m(n) by multiple regression analysis. To determine if the lack of G2m(n) was associated with increased susceptibility to infection, we compared the frequencies of various Ig allotypes in 98 children infected with Hib and 98 matched controls. Caucasian children with Hib infections other than epiglottitis were significantly more likely to lack the G2m(n) allotype than controls (P less than 0.05). G2m(n) negative Caucasian children less than or equal to 18 mo old have a 5.1-fold higher risk of nonepiglottitic Hib infections than G2m(n) positive children (P less than 0.01). We conclude that allotypic variants of the gamma-2 heavy chain genes, or genes in linkage equilibrium with them, exert a regulatory influence on the caucasian antibody response to a variety of immunologically distinct bacterial polysaccharide antigens. Young Caucasian children of the low responder phenotype, i.e., those lacking the G2m(n) allotype, are genetically predisposed to Hib and perhaps other bacterial infections.

Authors

D M Ambrosino, G Schiffman, E C Gotschlich, P H Schur, G A Rosenberg, G G DeLange, E van Loghem, G R Siber

Primate mammary development. Effects of hypophysectomy, prolactin inhibition, and growth hormone administration.

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Abstract

The pituitary gland has been found to be an important factor in mammary development in primates. Hypophysectomy in 12 sexually immature monkeys caused significant inhibition of estradiol (E2)-induced mammary growth and development. A histological index of mammary development in sexually immature hypophysectomized animals was lower (0.82) than in intact E2-treated controls (3.4; P less than 0.008). Hypophysectomy also inhibited growth of the mammary gland as judged by a size index. Despite the hypophysectomy, E2 stimulated some, albeit blunted, mammary growth and development, which may have been due to incomplete hypophysectomy. Selective inhibition of prolactin by ergot drugs in intact animals did not prevent full mammary development, suggesting that there may be pituitary mammogens other than prolactin, or that very low or unmeasurable concentrations of prolactin were sufficient to synergize with E2 to cause full acinar development. The mean histological index was 3.08 in E2-treated animals and 3.16 in animals treated with E2 plus pergolide. There was also no difference in the size of the glands. We evaluated the effect of growth hormone on mammary development by treating three hypophysectomized animals with pure 22,000 mol wt human growth hormone (hGH) (Genentech, Inc., South San Francisco, CA). We found that physiological or slightly supraphysiological concentrations of hGH in animals with unmeasurable prolactin were incapable of restoring the capacity of E2 to induce full mammary growth. These findings suggest that, if growth hormone is a mammary mitogen, that physiological concentrations are insufficient to synergize with E2 to induce full mammary growth or that other forms of hGH are mammogenic. Our studies suggest that the role of the pituitary gland in mammary mitogenesis in primates is more complicated than previously thought. They also raise the possibility that heretofore unidentified pituitary substances may be mammogenic.

Authors

D L Kleinberg, W Niemann, E Flamm, P Cooper, G Babitsky, Q Valensi

Electron microprobe analysis of human labial gland secretory granules in cystic fibrosis.

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Abstract

X-ray microanalysis of freeze-dried labial gland cryosections revealed that Na concentration was doubled and the Ca/S concentration ratio was decreased in secretory granules of labial glands from patients with cystic fibrosis (CF) when compared with glands from normal subjects. Other results suggested that the decrease in the Ca/S concentration ratio resulted from an increase in S concentration. These findings imply that mucous granules in labial saliva showed a CF-related increase in Na and S content, and such changes would be expected to affect the rheology of the mucus after exocytosis. In contrast with a previous study in human parotid glands, no evidence was found for CF-related changes in cytoplasmic or nuclear Na, K, and Ca concentrations. Significant elemental differences were found between secretory granules and nuclei and cytoplasm of control cells.

Authors

K Izutsu, D Johnson, M Schubert, E Wang, B Ramsey, A Tamarin, E Truelove, W Ensign, M Young

Sera from patients with the acquired immunodeficiency syndrome inhibit production of interleukin-2 by normal lymphocytes.

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Abstract

We studied the effects of sera from patients with the acquired immunodeficiency syndrome (AIDS) on interleukin-2 (IL-2) production to help elucidate the mechanism of immunodeficiency. Compared with sera from healthy controls, sera from AIDS patients suppressed phytohemagglutinin (PHA)-induced IL-2 production by normal blood mononuclear cells. Sera from homosexual contacts of AIDS patients and from adults with acute cytomegalovirus infection generally lacked this suppressive activity. The effect of the AIDS sera could not be attributed to absence of a stimulatory or nutritive factor, to inactivation of IL-2, to inhibition of the IL-2 assay, nor to increased turnover of IL-2. The suppressive effect of the sera was not mediated by radiosensitive or T8 antigen-bearing suppressor cells or by increased prostaglandin production or decreased interleukin-1 production. The sera acted directly on the groups of cells that produce IL-2, T cells and large granular lymphocytes; suppression occurred at an early, probably pretranslational, stage. When cells were incubated with AIDS sera and then washed, the suppressive effect persisted. The sera did not cause direct or complement-mediated cytotoxic effects on normal mononuclear cells nor did they suppress PHA-induced interferon production, nor proliferation of T lymphoblasts or lymphocyte lines. The suppressive effect was not mediated by interferon, cortisol, immunoglobulin G or M, or immune complexes. The activity was stable at pH 3, pH 10, and 60 degrees C; inactivated at 100 degrees C; and not ether extractable. Because IL-2 plays a central role in the development of many immune responses, the serum factor(s) that inhibits IL-2 production could contribute significantly to the immunodeficiency of AIDS.

Authors

J P Siegel, J Y Djeu, N I Stocks, H Masur, E P Gelmann, G V Quinnan Jr

Increased adherence of sickled and phosphatidylserine-enriched human erythrocytes to cultured human peripheral blood monocytes.

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Abstract

The precise mechanism by which sickle erythrocytes (RBC) are removed from the circulation is controversial, although it is possible that enhanced recognition of these cells by circulating mononuclear phagocytes could contribute to this process. We investigated this possibility by interacting sickle cells with cultured human peripheral blood monocytes. Our results show that both irreversibly sickled cells (ISC) and deoxygenated reversibly sickled cells (RSC) had a higher avidity for adherence to monocytes than did oxygenated sickle and normal RBC. ISC were the most adherent cell type. Adherence of RSC to monocytes was found to be reversible; reoxygenation of deoxygenated RSC resulted in a significant decrease in RSC--monocyte adherence. Concomitant with alterations in sickle RBC adherence were alterations in the organization and bilayer distribution of membrane phospholipids in these cells. Specifically, enhanced adherence was associated with increased exposure of RBC membrane outer leaflet phosphatidylserine (PS) and phosphatidylethanolamine, whereas lack of adherence was associated with normal patterns of membrane phospholipid distribution. To investigate the possibility of whether the exposure of PS in the outer membrane leaflet of these cells might be responsible for their recognition by monocytes, the membranes of normal RBC were enriched with the fluorescent PS analogue 1-acyl-2[(N-4-nitro-benzo-2-oxa-1,3-diazole)aminocaproyl]-phosphatidy lse rine (NBD-PS) via transfer of the exogenous lipid from a population of donor phospholipid vesicles (liposomes). RBC enriched with NBD-PS exhibited enhanced adherence to monocytes, whereas adherence of RBC enriched with similar amounts of NBD-phosphatidylcholine (NBD-PC) was not increased. Furthermore, preincubation of monocytes with PS liposomes resulted in a approximately 60% inhibition of ISC adherence to monocytes, whereas no inhibition occurred when monocytes were preincubated with PC liposomes. These findings strongly suggest that erythrocyte surface PS may be a ligand recognized by receptors on human peripheral blood monocytes and that abnormal exposure of PS in the outer leaflet of the RBC membrane, as found in sickle RBC, might serve to trigger their recognition by circulating monocytes. Our results further suggest that abnormalities in the organization of erythrocyte membrane phospholipids may have significant pathophysiologic implications, possibly including shortened cell survival.

Authors

R S Schwartz, Y Tanaka, I J Fidler, D T Chiu, B Lubin, A J Schroit

Fat cell metabolism in different regions in women. Effect of menstrual cycle, pregnancy, and lactation.

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Abstract

Adipose tissue lipolysis and lipoprotein lipase (LPL) activity were studied in biopsies from the femoral and abdominal depots in healthy women during early or late menstrual cycle, pregnancy, and the lactation period. When the differences in cell size were taken into account, basal lipolysis was similar in both regions in nonpregnant women. During lactation, however, lipolysis was significantly higher in the femoral region. The lipolytic effect of noradrenaline (10(-6) M) was significantly less in the femoral region in the nonpregnant women and during early pregnancy. However, the lipolytic response was the same in both regions in lactating women. LPL activity was higher in the femoral than in the abdominal region except during lactation when a marked decrease in the LPL activity was seen in the femoral region. The LPL activity in the abdominal region remained unchanged in all patient groups. The results imply that in both nonpregnant and pregnant women lipid assimilation is favored in the femoral depot. During lactation, however, the metabolic pattern changes; the LPL activity decreases and lipid mobilization increases in this depot. These changes are much less pronounced in the abdominal region. Thus, fat cells from different regions show a differential response during pregnancy and lactation. These results suggest that the adipose tissue in different regions may have specialized functions.

Authors

M Rebuffé-Scrive, L Enk, N Crona, P Lönnroth, L Abrahamsson, U Smith, P Björntorp

A human T cell lymphoma secreting an immunoglobulin E specific helper factor.

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Abstract

An 8-yr-old nonallergic girl with non-Hodgkin's lymphoma had markedly elevated serum IgE at presentation (greater than 10,000 IU/ml), negative skin tests to a battery of 24 common allergens, and no evidence of parasitic infestation. Serum levels of IgG, IgA, and IgM were normal. Remission after cytotoxic chemotherapy was accompanied by a marked reduction in serum IgE levels (to less than 200 IU/ml) with no change in the level of serum IgG, IgM, or IgA. Recurrence of the lymphoma 7 mo after remission was accompanied by an isotype specific rise in serum IgE (to 3,850 IU/ml). Isoelectric focusing revealed that the IgE was polyclonal. Phenotypic analysis of the lymphoma obtained during relapse revealed all (greater than 98%) cells to be T3+, T4+, and T8+. Incubation of lymphoma cells with human myeloma IgE followed by immunosorbent purified fluorescein tagged goat anti-human IgE (anti-IgE PS-adsorbed over IgE ADZ) stained 25% of the cells. In contrast, less than 1% of the cells were stained after incubation with human IgG followed by fluorescein conjugated goat anti-human IgE. Supernatants from lymphoma cells (5 X 10(6)/ml, 48 h) enhanced IgE production in B cells derived from four patients with allergic rhinitis (mean +/- SD picograms per milliliter of net IgE 930 +/- 320 in unstimulated cultures versus 2,450 +/- 650 in cultures stimulated with lymphoma supernatants; P less than 0.01) but did not induce IgE synthesis in B cells from two normal subjects that synthesized no IgE spontaneously. Lymphoma supernatants failed to enhance IgG synthesis by B cells of both allergic and nonallergic subjects. These results indicate that a T cell lymphoma comprised of cells bearing Fc receptors for IgE with a phenotype characteristic of immature T cells (i.e., T3+, T4+, T8+) exhibited IgE specific helper function. This lymphoma may represent the monoclonal expansion of a subpopulation of IgE specific helper T cells.

Authors

M C Young, H Harfi, R Sabbah, D Y Leung, R S Geha

Administration of atrial natriuretic factor inhibits sodium-coupled transport in proximal tubules.

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Abstract

The newly discovered peptides extracted from cardiac atria, atrial natriuretic factors (ANFs), when administered parenterally cause renal hemodynamic changes and natriuresis. The nephron sites and cellular mechanism accounting for profound increase in Na+ excretion in response to ANFs are not yet clarified. In the present study we investigated whether synthetic ANF peptide alters the reabsorption of Na+ and reabsorption of solutes cotransported with Na+ in the proximal tubules of rats. Synthetic ANF peptide consisting of 26 amino acids, 4 micrograms/kg body wt/h, or vehicle in controls, was infused to surgically thyroparathyroidectomized anesthetized rats. After determination of the fractional excretion (FE) of electrolytes (Na+, K+, Pi, Ca2+, Mg2+, HCO3), the kidneys were removed and luminal brush border membrane vesicles (BBMVs) were prepared from renal cortex. Solute transport was measured in BBMVs by rapid filtration techniques. Infusion of ANF peptide increased FENa, FEPi, and FEHCO3; but FECa, FEK, and FEMg were not changed. The increase in FENa was significantly correlated, on the one hand, with increase of FEPi (r = 0.9, n = 7; P less than 0.01) and with increase of FEHCO3 (r = 0.89, n = 7; P less than 0.01). On the other hand, FENa did not correlate with FEK, FECa, or with FEMg. The Na+ gradient-dependent uptake of Pi by BBMVs prepared from renal cortex of rats receiving ANF infusion was significantly (P less than 0.05) decreased (-25%), whereas the Na+ gradient-dependent uptake of L-[3H]proline and of D-[3H]glucose or the diffusional uptake of 22Na+ were not changed. ANF-elicited change in FEPi showed a close inverse correlation with decrease of Na+-dependent Pi uptake by BBMVs isolated from infused rats (r = 0.99, n = 7; P less than 0.001). Direct addition of ANF to BBMVs in vitro did not change the Na+ gradient-dependent Pi uptake. In rats infused with ANF, the rate of amiloride-sensitive Na+-H+ exchange across the brush border membrane (BBM) was significantly (P less than 0.05) decreased (-40%), whereas the diffusional 22Na+ uptake (0.5 min) and the equilibrium (120 min) uptake of 22Na+ were not changed. The inhibition of Na+-H+ exchange after ANF was likely due to alteration of the BBM antiporter itself, in that the H+ conductance of BBMVs was not increased. We conclude that synthetic ANF (a) decreases tubular Na+ reabsorption linked to reabsorption of HCO3 in proximal tubules, and (b) inhibits proximal tubular reabsorption of Pi coupled to Na+ reabsorption, independent of secretion and/or action of parathyroid hormone or calcitonin. These ANF effects are associated with inhibition of Na+-Pi synport and of Na+-H+ antiport in luminal BBMs. Our findings document that inhibition of Na+-coupled transport processes in proximal tubules is an integral part of the renal response to ANF.

Authors

T G Hammond, A N Yusufi, F G Knox, T P Dousa

Adoptive transfer of suppression of arthritis in the mouse model of collagen-induced arthritis. Evidence for a type II collagen-specific suppressor T cell.

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Abstract

This study details the suppressive mechanism involved in the antigen-specific suppression of collagen-induced arthritis. Intravenous injection of 500 micrograms of soluble native type II collagen 3 d before immunization with native type II collagen emulsified in complete Freund's adjuvant resulted in animals with decreased in vitro cellular and humoral immune response to native and denatured type II collagen compared with control groups. Control groups were composed of animals preinoculated with saline and type I collagen and established the antigen-specific nature of the observed suppression. Mice with reduced immune responses to type II collagen also were observed to portray little or no erythema and edema associated with collagen-induced arthritis. Adoptive transfer experiments established the requirement of T cells for the suppression of collagen-induced arthritis. Analysis of the phenotype of responding splenic cells in chronic immunotherapeutically suppressed mice in vitro revealed that responding cells were Ly1-2+ (suppressor/cytotoxic) T cells. On the other hand, the cellular phenotype of T cells responding to type II collagen in nonsuppressed collagen-induced arthritic mice was Ly1+2- (helper/inducer T cells). The data indicate that type II collagen-specific T cells are generated on intravenous inoculation of soluble native type II collagen. These cells are observed in type II collagen-immune animals, which are nonarthritic and portray reduced humoral and in vitro cellular immune response to type II collagen. This study suggests that specific suppression of immune responses to type II collagen by T-suppressor cells can be immunotherapeutic in certain forms of arthritis.

Authors

T F Kresina, R W Moskowitz

Influence of cell cycle phase-specific agents on simian fetal hemoglobin synthesis.

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Abstract

To determine the influence of cell cycle-specific agents on primate hematopoiesis and fetal hemoglobin production, two juvenile cynomolgus monkeys (Macaca fascicularis) were repeatedly bled to maintain their hemoglobins at approximately 6.5 g/dl and fetal hemoglobin levels at 3-5%. Six separate 5-d courses of hydroxyurea at 100 mg/kg per d were then administered over the next 200 d while phlebotomy was continued. These courses of hydroxyurea progressively raised the fetal hemoglobin levels to 17 and 18%, respectively. The drug had very little effect on the frequency of immature erythroid progenitors (BFU-E) in the bone marrow, but caused a marked reduction in the frequency of later progenitors (CFU-E) and a transient fall in the reticulocyte count. Following the courses of hydroxyurea, the number of F cells and the fetal hemoglobin level fell to base line over a period of 4 wk. Two control animals which were not phlebotomized showed no detectable increase in F cells or fetal hemoglobin when treated with the same regimen of hydroxyurea. A 5-d course of 5-azacytidine at 8 mg/kg per d was then given to each of the phlebotomized animals. This produced a more profound, albeit transient, reticulocytopenia, a fall in the CFU-E/BFU-E ratio, and a prompt increase in the fetal hemoglobin to levels even higher than were seen following a single 5-d course of hydroxyurea at 100 mg/kg/d. Subsequently, the animals were given a single dose of vinblastine at 0.4 mg/kg which reduced reticulocytes and CFU-E to the same extent as hydroxyurea; however, vinblastine at this dose had no effect on hemoglobin F (HbF) production. In contrast, when vinblastine was administered to the phlebotomized monkeys as a 5-d course at 0.2 mg/kg/d, prolonged reticulocytopenia followed by dramatic F cell and HbF responses were seen. Combinations of single dose vinblastine and a 5-d course of hydroxyurea were subsequently administered using two different schedules. When the animals received vinblastine on the first day of a 5-d course of hydroxyurea, the F cell response was double that seen following hydroxyurea treatment alone. In contrast, when vinblastine was administered on the final day of hydroxyurea treatment, the magnitude of the F cell response was the same as that which occurred following hydroxyurea treatment alone, but the onset of the rise was delayed for 4 d and HbF/F cell response was much higher. These results establish several important features of the fetal hemoglobin response to cytotoxic agents in the primate model. The response requires accelerated erythropoiesis and is preceded by transient reticulocytopenia. The response is produced by S phase- and M phase-specific agents when given in sufficient doses and at appropriate schedules. Passage of erythrocyte progenitors through M phase appears to be necessary for expression of the effect produced by S phase agents. The fetal hemoglobin response induced by cytotoxic drug administration occurs during the recovery of erythropoiesis following marrow suppression.

Authors

N L Letvin, D C Linch, G P Beardsley, K W McIntyre, B A Miller, D G Nathan

Metabolism of heptadecapeptide gastrin in humans studied by region-specific antisera.

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Abstract

The metabolism of synthetic human heptadecapeptide gastrin (G17) in vivo, and in serum in vitro, was studied by radioimmunoassay using region specific antisera, gel filtration, ion exchange chromatography, and high performance liquid chromatography. After infusion of G17 intravenously in normal human volunteers, COOH-terminal and NH2-terminal immunoreactive G17 fragments were generated. At a steady state, approximately 15% of COOH-terminal immunoreactivity was attributable to G14-like material and up to 25% of total NH2-terminal immunoreactivity was attributable to two NH2-terminal fragments; one had the chromatographic properties of 1-13 G17, and the other was less acidic and less hydrophobic. After stopping the infusion of G17, the latter fragments accounted for progressively greater proportions of total gastrin activity. When G17 was incubated in serum in vitro, there was time-dependent and temperature-dependent loss of immunoreactivity, and again COOH-terminal and NH2-terminal immunoreactive fragments were formed. Removal of the NH2-terminal pyroglutamic acid was probably the rate limiting step because synthetic 2-17 G17 was degraded more rapidly in serum (t1/2, 2-3 h) than G17 (t1/2, 3-5 h). EDTA blocked degradation at the COOH-terminus of both 2-17 G17 and G17 but cleavage at the NH2-terminus still occurred, giving rise to a G14-like peptide. The rate of conversion of G17 in serum was not enough to account for the production of fragments in vivo, and it is proposed that these are formed when G17 encounters enzymes on cell surfaces, perhaps during passage through the capillary circulation. The production of these fragments needs to be considered in interpreting studies of the identity, metabolism, and release of gastrin in health and disease.

Authors

S Pauwels, G J Dockray, R Walker, S Marcus

Abnormal sodium transport in synaptosomes from brain of uremic rats.

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Abstract

The causes of central nervous system (CNS) dysfunction in uremia are not well known and are not completely reversed by dialysis. This problem was investigated in synaptosomes, which are membrane vesicles from synaptic junctions in the brain. We measured Na uptake under conditions of control, veratridine stimulation, and tetrodotoxin inhibition, in synaptosomes from normal and acutely uremic (blood urea nitrogen, 250 mg/dl) rats. In the control state, maximal Na uptake was 2.2 +/- 0.2 and 1.9 +/- 0.3 nmol/mg of protein in normal and uremic synaptosomes, respectively. With veratridine stimulation, Na uptake was increased by 1.9 and 3.6 nmol/mg of protein in normal vs. uremic rats (P less than 0.001). The increased veratridine-stimulated Na uptake observed in uremia could be due either to increased membrane permeability to Na or decrease in the Na-K ATPase pump activity. To investigate this, we studied the Na-K ATPase pump function by evaluating uptake of K (using rubidium as a tracer), uptake of Na during ATP stimulation, and inhibition of Rb and Na uptake by ouabain. In uremic rats both Rb uptake and ATP-stimulated Na uptake were significantly less than in normals (P less than 0.005). This suggests a defect in the Na-K ATPase pump. Membrane permeability for Na was then evaluated both by measuring initial Na uptake, and with addition of valinomycin. No change in Na uptake pattern was observed with valinomycin, and initial Na uptake was not significantly different in normal versus uremic synaptosomes. These data show that (a) in uremic rats veratridine-stimulated Na accumulation is significantly greater than normal; (b) the increased Na accumulation observed in uremia appears to be due to alterations in Na-K ATPase pump activity; and (c) the altered Na accumulation observed is probably not due to a uremic environment, but may be secondary to a physiologic alteration in synaptosomal function due to the uremic state. These abnormalities may affect neurotransmission and may be associated with the CNS alterations observed in uremia.

Authors

C L Fraser, P Sarnacki, A I Arieff

Abnormal function of B lymphocytes from peripheral blood of multiple myeloma patients. Lack of correlation between the number of cells potentially able to secrete immunoglobulin M and serum immunoglobulin M levels.

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Abstract

Multiple myeloma patients are deficient in normal polyclonal serum immunoglobulins. To determine the reasons for this decrease, we quantitated and compared the number of surface IgM+ B lymphocytes, and the number of B cells susceptible to transformation by Epstein-Barr virus (EBV) with the concentration of IgM in serum. Serum IgM levels varied considerably in individual patients, temporally shifting from undetectable to normal amounts and then dropping again to undetectable levels. A transient rise to normal serum IgM concentrations was seen in 42% of patients assessed at two or more time points. Of 44 patients, 52% showed a lack of correlation between the number of surface IgM+ (sIgM+) B cells and serum IgM concentration. One subset of patients (25%) had detectable to normal numbers of sIgM+ B cells in blood but undetectable levels of serum IgM. Transformation of B cells from these patients indicated a block in IgM secretion that was extrinsic to the B cells that were fully able to transcribe, translate, and secrete IgM after EBV transformation. A second subset of patients (27%) had undetectable numbers of sIgM+ B cells but near normal levels of serum IgM, suggesting abundant secretion by few clones of B cells. Of 18 patients with monoclonal gammopathy of undetermined significance (MGUS), 26% showed a lack of correlation between the numbers of sIgM+ B cells and serum IgM concentration. We suggest that in patients with multiple myeloma, and in some with MGUS, there exists a mechanism(s) extrinsic to the B cell that mediates an arrest in terminal B lymphocyte maturation.

Authors

L M Pilarski, B A Ruether, M J Mant

Human alveolar macrophages synthesize factor VII in vitro. Possible role in interstitial lung disease.

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Abstract

Both fibrin and tissue macrophages are prominent in the histopathology of chronic inflammatory pulmonary disease. We therefore examined the procoagulant activity of freshly lavaged human alveolar macrophages in vitro. Intact macrophages (5 X 10(5) cells) from 13 healthy volunteers promoted clotting of whole plasma in a mean of 65 s. Macrophage procoagulant activity was at least partially independent of exogenous Factor VII as judged by a mean clotting time of 99 s in Factor VII-deficient plasma and by neutralization of procoagulant activity by an antibody to Factor VII. Immunoprecipitation of extracts of macrophages metabolically labeled with [35S]methionine by Factor VII antibody and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a labeled protein consistent in size with the known molecular weight of blood Factor VII, 48,000. The addition of 50 micrograms of unlabeled, purified Factor VII blocked recovery of the 48,000-mol wt protein. In addition, supernatants of cultured macrophages from six normal volunteers had Factor X-activating activity that was suppressed an average of 71% after culture in the presence of 50 microM coumadin or entirely by the Factor VII antibody indicating that Factor VII synthesized by the cell was biologically active. Endotoxin in vitro induced increases in cellular tissue factor but had no consistent effect on macrophage Factor VII activity. We also examined the tissue factor and Factor VII activities of freshly lavaged alveolar cells from nine subjects with clinical and/or histologic evidence of sarcoidosis. Four of the nine subjects expressed increased tissue factor and seven of nine had increased Factor VII activity over the normal range (P less than 0.01). We estimate the mean Factor VII associated with the cells of sarcoid patients to be 4.7 ng/10(6) cells (range 0.4-20) as compared to a mean of 0.74 ng/10(6) cells (range 0.2-2) for that of normal subjects. Along with previous data showing synthesis of plasminogen activator, these findings indicate that human alveolar macrophages normally synthesize and express measurable amounts of the initial enzymes of proteolytic reactions regulating both fibrin deposition and fibrin resorption. Abnormalities in Factor VII activity in a small group of patients with sarcoidosis raise the possibility that modulation of fibrin turnover by macrophages may contribute to the pathology of this and perhaps other interstitial lung diseases.

Authors

H A Chapman Jr, C L Allen, O L Stone, D S Fair

Sympathetic modulation of biochemical and physiological response to immune degranulation in canine bronchial airways in vivo.

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Abstract

The effect of sympathetic stimulation on bronchial smooth muscle contractile response after mast cell degranulation with Ascaris suum antigen was studied in 36 natively allergic dogs in situ. Bronchial smooth muscle response was measured isometrically in a single right middle lobe bronchus. A dose of antigen causing maximal release of mediator was administered to the bronchus through the bronchial arterial circulation. Serial plasma histamine concentrations were determined at 15-s intervals after intra-arterial (i.a.) administration of antigen. Samples of blood were obtained simultaneously from right heart and femoral artery, and arteriovenous difference (AVd) in histamine concentration across the bronchus was determined during mast cell degranulation. In nine dogs showing bronchial mast cell degranulation to antigen challenge, bronchial smooth muscle contraction was 22.3 +/- 2.95 g and the mean AVd in histamine concentration across the bronchus was 188 +/- 41.5 ng/ml. Six other dogs having muscarinic blockade with 0.75-1.0 mg/kg intravenous atropine were given i.a. antigen after 1 min of steady-state sympathetic stimulation with intravenous 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP). Sympathetic stimulation during Ascaris suum antigen challenge caused complete inhibition of bronchial smooth muscle contractile response to i.a. antigen (P less than 0.001), and a significant AVd in histamine concentration across the bronchus (9.8 +/- 16.0 ng/ml; P less than 0.01 vs. control) was not detected. Peak plasma histamine concentration in control dogs was 1,138 +/- 237 ng/ml vs. 310 +/- 135 ng/ml in animals receiving sympathetic stimulation (P less than 0.01). In four dogs undergoing systemic anaphylaxis to i.v. antigen, subsequent sympathetic stimulation with i.v. DMPP reduced bronchomotor tone to approximately 70% of base-line control. Exogenously induced sympathetic stimulation can substantially inhibit systemic mast cell degranulation to Ascaris suum antigen in allergic dogs. Maximal stimulation of the sympathetic nervous system causes substantial inhibition of respiratory mast cell secretion of histamine and bronchial smooth muscle contraction to circulating mediator.

Authors

E R Garrity, N P Stimler, N M Munoz, J Tallet, A C David, A R Leff

Modulation of proinsulin messenger RNA after partial pancreatectomy in rats. Relationships to glucose homeostasis.

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Abstract

These studies of partial pancreatectomy assess pancreatic proinsulin messenger RNA (mRNA) levels as an index of in vivo insulin biosynthesis, and show relationships to glucose homeostasis. Rats were subjected to sham operation, 50% pancreatectomy (Px), or 90% Px, and were examined after 1, 3, or 14 wk. Proinsulin mRNA was measured by dot hybridization to complementary DNA. After 50% Px there was a nearly complete adaptation of proinsulin mRNA. After 90% Px a marked increase of proinsulin mRNA occurred, but it was insufficient and it was not maintained with time. The deficit in insulin production is related to development of hyperglycemia. Sham-operated controls showed no worsening of fasting or fed blood glucose or of intraperitoneal glucose tolerance within the period of observation. Total proinsulin mRNA and pancreatic insulin content rose in proportion to body weight. 50% Px produced no change from controls in body weight or blood glucose. The concentration of proinsulin mRNA in the 50% pancreatic remnant paralleled that of controls after 1 and 3 wk, but then increased after 14 wk, such that total proinsulin mRNA approached control levels. This adaptive response was reflected by changes in serum insulin, but not by pancreatic insulin content, which was only 30% of control after 14 wk. Intraperitoneal glucose tolerance was impaired mildly, and did not worsen with time after pancreatectomy. 90% Px led to elevated fed blood glucose and reduced serum insulin after 3 wk, and fasting hyperglycemia was seen after 14 wk. Proinsulin mRNA concentration in the 10% pancreatic remnant showed an adaptive increase after 1 and 3 wk, such that total proinsulin mRNA reached 40% of control. After 14 wk, however, remnant proinsulin mRNA concentration was no longer increased; total proinsulin mRNA and pancreatic insulin content were severely reduced. Intraperitoneal glucose tolerance was impaired more dramatically than with the 50% Px animals, and worsened with time after operation. These observations indicate ability to increase proinsulin mRNA levels as an adaptation to pancreatectomy. Insufficiency of this adaptation is associated with the development of hyperglycemia, and the loss of this adaptation correlates with a worsening of glucose tolerance.

Authors

M J Orland, R Chyn, M A Permutt

Cyclic adenosine monophosphate-stimulated bicarbonate secretion in rabbit cortical collecting tubules.

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Abstract

We studied the effects of cyclic AMP (cAMP) on HCO-3 transport by rabbit cortical collecting tubules perfused in vitro. Net HCO-3 secretion was observed in tubules from NaHCO3- loaded rabbits. 8-Bromo-cAMP-stimulated net HCO-3 secretion, whereas secretion fell with time in control tubules. Both isoproterenol and vasopressin (ADH) are known to stimulate adenylate cyclase in this epithelium; however, only isoproterenol stimulated net HCO-3 secretion. The mechanism of cAMP-stimulated HCO-3 secretion was examined. If both HCO-3 and H+ secretion were to occur simultaneously in tubules exhibiting net HCO-3 secretion, cAMP might increase the net HCO-3 secretory rate by inhibiting H+ secretion, by stimulating HCO-3 secretion, or both. These possibilities were examined using basolateral addition of the disulfonic stilbene (4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS). In acidifying tubules from NH4Cl-loaded rabbits, DIDS eliminated HCO-3 reabsorption, a result consistent with known effects of DIDS as an inhibitor of H+ secretion. In contrast, cAMP left acidification (H+ secretion) intact. DIDS applied to HCO-3 secretory tubules failed to increase the HCO-3 secretory rate, indicating minimal H+ secretion in HCO-3 secreting tubules. Thus, inhibition of H+ secretion by cAMP could not account for the cAMP-induced stimulation of net HCO-3 secretion. cAMP-stimulated HCO-3 secretion was reversibly eliminated by 0 Cl perfusate, whereas luminal DIDS had no effect. Bath amiloride (1 mM) failed to eliminate cAMP-stimulated HCO-3 secretion when bath [Na+] was 145 mM or 5 mM. cAMP depolarized the transepithelial voltage. The collected fluid [HCO-3] after cAMP could be accounted for by electrical driving forces, suggesting that cAMP stimulates passive HCO-3 secretion. However, cAMP did not alter HCO-3 permeability measured under conditions expected to inhibit transcellular HCO-3 movement (0 Cl- solutions and bath DIDS). This measured HCO-3 permeability was not high enough to account, by passive diffusion, for the HCO-3 fluxes observed in Cl-containing solutions. We conclude the following: cAMP increased net HCO3- secretion by stimulating HCO3- secretion and not by inhibiting H+ secretion; this HCO3- secretion may have occurred by Cl-HCO3- exchange; Na+-H+ exchange appeared not to play a role in basolateral H+ extrusion under these conditions; and the stimulation of HCO3- secretion by isoproterenol, but not ADH, suggests the existence of separate cell cAMP pools or cellular heterogeneity in this cAMP response.

Authors

V L Schuster

Platelet thrombospondin forms a trimolecular complex with plasminogen and histidine-rich glycoprotein.

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Abstract

Thrombospondin (TSP), a multifunctional alpha-granule glycoprotein of human platelets binds fibrinogen, fibronectin, heparin, histidine-rich glycoprotein (HRGP), and plasminogen (Plg), and thus, may play an important role in regulating thrombotic influences at vessel surfaces. In this study we have demonstrated that purified human platelet TSP formed a trimolecular complex with human Plg and HRGP. Complex formation was detected by a specific binding enzyme-linked immunosorbent assay (ELISA) which demonstrated simultaneous binding of fluid-phase Plg and HRGP to TSP adsorbed to microtitration wells. While neither ligand inhibited complex formation of the other with TSP, 10 mM epsilon-amino-n-caproic acid selectively blocked incorporation of Plg into the complex, suggesting that TSP contains independent binding sites for Plg and HRGP. Comparable extent of trimolecular complex formation was also detected when TSP monomer was substituted for whole TSP in the ELISA. HRGP covalently cross-linked to Sepharose 4B simultaneously bound both 125I-TSP and 131I-Plg, confirming trimolecular complex formation. Rocket immunoelectrophoresis of mixtures of the purified radiolabeled proteins into anti-Plg containing agarose also confirmed trimolecular complex formation. The TSP-HRGP-Plg complex bound a similar amount of heparin as the TSP-HRGP complex, demonstrating that the HRGP within the trimolecular complex maintained functional capability. Similarly, using a fluorometric plasmin substrate, the trimolecular complex was shown to be an effective substrate for tissue plasminogen activator. Significant amounts of plasmin were generated from the TSP-HRGP-Plg complex (equivalent to that from the TSP-Plg complex), but the rate of plasmin generation from the trimolecular complex was greater than from the bimolecular complex, suggesting an important interaction of HRGP with Plg when both are complexed to TSP. The macromolecular assembly of these three proteins on cellular surfaces, such as the platelet, may serve important regulatory functions, both prothrombotic at sites of active fibrin deposition and proteolytic in nonfibrin-containing microenvironments.

Authors

R L Silverstein, L L Leung, P C Harpel, R L Nachman

Characterization of the complement sensitivity of paroxysmal nocturnal hemoglobinuria erythrocytes.

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Abstract

The affected erythrocytes of paroxysmal nocturnal hemoglobinuria (PNH II and PNH III cells) are abnormally sensitive to complement-mediated lysis. Normal human erythrocytes chemically modified by treatment with 2-amino-ethylisothiouronium bromide (AET) have been used as models for PNH cells inasmuch as they also exhibit an enhanced susceptibility to complement. To investigate the bases for the greater sensitivity of these abnormal cells to complement-mediated lysis, we compared binding of C3 and constituents of the membrane attack complex to normal, PNH II, PNH III, and AET-treated cells after classical pathway activation by antibody and fluid-phase activation by cobra venom factor complexes. When whole serum complement was activated by antibody, there was increased binding of C3 and C9 to PNH II, PNH III, and AET-treated cells, although the binding of these complement components to PNH II and PNH III cells was considerably greater than their binding to the AET-treated cells. In addition, all of the abnormal cell types showed a greater degree of lysis per C9 bound than did the normal erythrocytes. PNH III and AET-treated cells were readily lysed by fluid-phase activation of complement, whereas normal and PNH II erythrocytes were not susceptible to bystander lysis. The greater hemolysis of PNH III and AET-treated cells in this reactive lysis system was due to a quantitative increase in binding of constituents of the membrane attack complex. This more efficient binding of the terminal components after fluid-phase activation of whole serum complement was not mediated by cell-bound C3 fragments. These investigations demonstrate that the molecular events that characterize the enhanced susceptibility of PNH II, PNH III, and AET-treated erythrocytes to complement-mediated lysis are heterogeneous.

Authors

C J Parker, T Wiedmer, P J Sims, W F Rosse

Extracellular matrix promotes the growth and differentiation of murine hematopoietic cells in vitro.

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Abstract

We have developed a long-term culture system in which murine marrow cells are cultured on a complex extracellular matrix (ECM) that is derived from marrow and extracted with guanidine hydrochloride and dithiothreitol. Marrow cultures were established with fresh murine marrow cells and recharged at 2 wk (week 0). Phase microscopy showed a dramatically increased adherent cell layer development on ECM compared with controls within a week after recharge. By electron microscopy, this adherent layer was composed of numerous reticular cells apparently attached to the ECM which extended cytoplasmic projections to the surrounding hematopoietic cells. Adherent cellularity on ECM-coated dishes increased to 30 times the control values by week 2. Cumulative suspension cells on ECM dishes were eight times controls. ECM influenced both hematopoietic progenitor cell proliferation and differentiation. Adherent colony-forming unit-granulocyte/macrophage and colony-forming unit-megakaryocyte were greater than 30 and 15 times the control values, respectively, by week 2 (P less than or equal to 0.05). There were more mature granulocytic and megakaryocytic cells in ECM-coated dishes than in controls at all time points. This new culture system directly demonstrates that ECM is an important component of the hematopoietic microenvironment.

Authors

A Campbell, M S Wicha, M Long

Prevention of autoantibody formation and prolonged survival in New Zealand black/New Zealand white F1 mice fed dehydroisoandrosterone.

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Abstract

Dehydroisoandrosterone, administered orally to New Zealand Black/New Zealand White F1 hybrid mice, prevented the formation of antibodies to double-stranded DNA and prolonged survival in this murine model of lupus erythematosus.

Authors

J A Lucas, S A Ahmed, M L Casey, P C MacDonald